This application relates to and cross-references U.S. patent application entitled xe2x80x9cMETHOD AND SYSTEM FOR OPERATING TWO OR MORE INTEGRATORS WITH DIFFERENT POWER SUPPLIES FOR AN ANALOG-TO-DIGITAL DELTA-SIGMA MODULATORxe2x80x9d, (Ser. No. 09/843,393), which was contemporaneously filed on the same date as the present application. The present patent application also cross-references U.S. patent application Ser. No. 09/633,505 filed on Aug. 7, 2000 to John Melanson entitled xe2x80x9cSECOND AND HIGHER ORDER DYNAMIC ELEMENT MATCHING IN MULTIBIT DIGITAL TO ANALOG AND ANALOG TO DIGITAL CONVERTERSxe2x80x9d (hereafter referred to as xe2x80x9cfirst DEM patent applicationxe2x80x9d), which has been assigned to CIRRUS LOGIC, INC., Austin, Tex., and U.S. patent application Ser. No. 09/633,381 filed on Aug. 7, 2000 to John Melanson entitled xe2x80x9cMULTILEVEL ANALOG TO DIGITAL DATA CONVERTER HAVING DYNAMIC ELEMENT MATCHING IN A REFERENCE PATHxe2x80x9d (hereafter referred to as xe2x80x9csecond DEM patent applicationxe2x80x9d), which has also been assigned to CIRRUS LOGIC, INC., Austin, Tex. The above patent applications are incorporated by reference herein in their entirety.
1. Technical Field
The present invention relates in general to an analog-to-digital converter (xe2x80x9cADCxe2x80x9d), and, in particular, to a modulator for an ADC. Still more particularly, the present invention relates to a method and system for operating two or more components of a dynamic element matching (DEM) system with different power supplies. The DEM system may be used in a delta-sigma modulator of an ADC.
2. Description of the Related Art
Analog-to-digital converters (xe2x80x9cADCsxe2x80x9d) are used to convert an analog signal to a digital signal for digital processing and/or storage. ADCs are well known in the art and are used in a variety of applications. An ADC generally has an analog system and a digital system coupled to each other. The analog system includes at least a modulator for modulating the input analog signal. The analog system processes and converts an analog input signal to a digital output signal. The digital system processes and outputs the digital signal.
The modulator may be a delta-sigma modulator, which operates to digitize an analog input signal for the ADC. A delta-sigma modulator for the ADC generally includes at least an integrator (e.g., a filter), a summation circuit, and a quantizer coupled together. The integrator performs integration operations on the input signal while the summation circuit adds the integrated signals from the integrator. Some delta-sigma modulators have multiple integrators, which provide multiple stages of integration. The quantizer operates to quantify the added outputs from the summation circuit to provide a digitized signal.
The performance of a delta-sigma ADC is sensitive to the linearity of the digital-to-analog converter (xe2x80x9cDACxe2x80x9d) in the delta-sigma feedback path. Errors in the feedback path are not typically shaped out of the delta-sigma loop. One approach to achieving high DAC linearity may be to use an inherently linear single bit DAC. However, single bit modulators suffer from disadvantages in the loop stability, first integrator design, tonal characteristics, and decimation filter design. Another approach may be to use a multi-bit DAC that is linearized in the signal band by dynamic element matching (xe2x80x9cDEMxe2x80x9d). In this other approach, digital-to-analog converter (xe2x80x9cDACxe2x80x9d) elements are coupled in the feedback loop between the quantizer and the summation circuit. The DAC elements operate to convert the signals back from digital signals to analog signals. Typically, each DAC element is not exactly identical in specification to the other DAC elements. For example, the capacitor or resistor values for DAC elements supposedly having the same values generally do not exactly have the same values since small variations among component values usually exist. The element mismatches that cause non-linearity are noise shaped out of the signal band. A dynamic element matching (xe2x80x9cDEMxe2x80x9d) system is coupled in the feedback loop before the DAC elements. A DEM system changes how each element is used to represent a value in order to xe2x80x9cnoise shapexe2x80x9d the errors caused by mismatches from the signal band. The first and second DEM patent applications, which were cross-referenced and incorporated by reference earlier, disclose exemplary DEM systems.
The DEM system is used to track, equalize, and average usage of the DAC elements to minimize the effects of the mismatched component values for the DAC elements. The DEM system also linearizes operations of the DAC elements. The DEM typically includes a connection system/box, that enables the physical connections and implementation and usage of the DAC elements, and a connection calculator, which calculates and orders which DAC elements to be used at different times. The DEM system may have a thermometer code signal (e.g., an output signal of the DEM system) that is input into the connection system/box where the input is stirred or rearranged, and the connection system/box outputs the stirred/rearranged signal to the DAC elements. The state or address of the connection system/box is determined mathematically based on a previous state and the data that is sent to a connection calculator.
Typically, a single power supply drives all components or elements of a delta-sigma modulator. For example, the same power supply would drive all of the integrators, summation circuit, quantizer, DAC elements, and the DEM system of the delta-sigma modulator. Modulator technology has developed such that a large power voltage, such as five (5) volts or higher, is able to drive the modulator. The large power voltage allows the ADC to receive and process analog input signals in a wide voltage range, which results in the ADC having a wider dynamic range and a higher signal-to-noise ratio. However, physically large components, such as large-sized transistors, are needed for the ADC to operate under the large voltage. The use of physically large components makes the size and cost of the ADC chip respectively larger and higher. Also, since a large power voltage drives the modulator components, then the ADC consumes greater overall power.
The present invention recognizes the need to maintain a large power voltage driving the delta-sigma modulator so that at least a wider dynamic range and a higher signal-to-noise ratio is provided for the ADC. Furthermore, the present invention also recognizes the continual need and desire to reduce the overall physical size, cost, and power consumption of an ADC.
A method and system of operating dynamic element matching (xe2x80x9cDEMxe2x80x9d) components of a DEM system with two or more power supplies are disclosed. A connection system of the DEM system is driven with one power supply operating at one voltage. Connection system couples to components that are to be matched and equalized in usage by ordering outputs to components and activating the components according to ordered outputs. A connection calculator of the DEM system is driven with another power supply operating at another voltage different from the one voltage. Connection calculator is coupled to the connection system, and connection calculator calculates an order of usage of components. A level shifter system level shifts voltage levels of signals from connection system to connection calculator, and another level shifter system level shifts voltage levels of signals from connection calculator to connection system.
The above as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description.